You don't understand the difference between "federal" and "national."
The Garda Siochana is a national police force. By Irish law, all police in Ireland, local, county, provincial, and national fall under the authority of the Gardai.
The Bundespolizei are a national police force. By German law, for example, the Munich city cops are Bundespolizei, as is every cop in Germany. They ultimately answer to the commander of the Bundespolizei and Kanzlerin Merkel, not to the mayor of Munich.
The RCMP, oddly, is not. The structure of policing in Canada allows each province to establish its policing policy. All but Quebec and Ontario choose to contract the RCMP to provide provincial policing. But they don't have to, as the OPP and Surete Quebec demonstrate.
There is no national police force in the United States. If there is a dominant legal model for policing structure, it is the State. Each state legislature has the power to authorize subordinate jurisdictions (counties, cities, townships) to organize police forces, but they don't have to. The Congress has no power to bring policing under a single, national structure. Director Comey of the FBI has absolutely no authority whatever over the part-time marshal of Left Buttock, Montana or an officer in the NYPD.
Hope that helps.
